Co-assigned U.S. Pat. No. 9,185,291 teaches a zoom dual-camera system with smooth transition between two sub-cameras in video mode during zooming-in and zooming-out. Exemplarily, one sub-camera is a “Wide” sub-camera with a Wide field of view (FOVW) and the other sub-camera is a “Tele” sub-camera with a Tele FOV (FOVT) narrower than FOVW.
In known art, optical zoom is achieved in video mode “without fusion”, by switching between frames of the two sub-cameras. To avoid discontinuities in video mode, the switching includes applying additional processing blocks, for example image scaling and shifting. When zooming-in or zooming-out, the transition from one sub-camera to the other sub-camera occurs within one frame. For example, when a user-determined (or “user-defined”) zoom factor (ZF) is below a certain threshold denoted ZF_transition_threshold, the dual-camera image output to the observer (i.e. the image seen by the observer, also referred the as “camera output image”) is taken from a stream of frames output by one sub-camera, with additional processing applied to it, including shift, scale, color correction, white balance, etc. When the user-determined ZF is equal to or greater than ZF_transition_threshold, the camera output image is taken from is taken from a stream of frames output by the other sub-camera, with additional processing applied to it, including shift, scale, color correction, white balance, etc.
This shift in sub-camera output can result in a discontinuity observed by the observer in the stream of camera output images when the transition occurs. This discontinuity may be visible in object position change, point of view shift, color change, etc. In known art, this discontinuity is minimized by applying shift, scale, color correction etc. to the stream of frames from the two sub-cameras. While solutions to mitigate the discontinuity effect have been suggested by at least some of the present inventors, e.g. in U.S. Pat. No. 9,185,291, improvements in the transition process to further mitigate the discontinuity are still required.